Smoking marijuana can be dangerous and lead to substance abuse. A 20-year research reveals that cannabis may cause mental health problems.

Professor Wayne Hall, director of the Centre for Youth Substance Abuse Research at the University of Queensland and author of the study, reveals that one in 10 regular marijuana users become dependent on the drug.

The study, undertaken from 1993 to 2003, sheds light on the effects of drug usage on the general well-being and health of humans. Hall found that youngsters using cannabis on a regular basis are twice more likely to drop out of school compared to non-users. Regular cannabis users are also at higher risks of developing cognitive impairments as adults. Use of cannabis may also lead to the use of other illicit drugs in adulthood.

"There have been consistent associations found between regular (especially daily) cannabis use and adverse health and psychosocial outcomes, relationships that have often shown dose-response relationships, and that have persisted after statistical adjustment for plausible confounding factors," the study claims.

Hall also stated that marijuana is not as dangerous as heroin or cocaine, but regular use of the drug can still cause mental health problems. Regular marijuana users can experience psychotic symptoms such as hallucinations, delusions and disordered thinking. Findings reveal that 14 in 1,000 regular cannabis users may experience these symptoms compared to seven in 1,000 non-users.

The researchers also cite a separate study based in Sweden, which involved more than 50,000 youngsters. The study found that youngsters who had used marijuana at least 10 times by the time they were 18 years old were two times more likely to be treated with schizophrenia within the next 15 years of life, compared to non-users. The researchers believe that 13 percent of all schizophrenia cases may have been prevented if cannabis use was totally stopped.

The feeling of joy and relaxation after having cannabis comes from an ingredient called tetrahydrocannabinol (THC). Hall also points out that the THC content of marijuana has increased from two percent in the 1980s to about 8.5 percent in recent years. However, it remains unclear if the increase in THC content has any health effects on humans.

Critics have argued that other factors apart from cannabis usage may also play a role in the mental well-being of a person. It is also possible that people with mental health problems are more likely to use marijuana than others.